Steam generating and superheating units



Aug. 14, 1962 u. o. BLOMQUIST STEAM GENERATING AND SUPERHEATING UNITS 2 Sheets-Sheet 1 Filed June 6, 1958 Aug. 14, 1962 u. o. BLOMQUIST 3,049,104

STEAM GENERATING AND SUPERHEATING UNITS Filed June 6, 1958 2 Sheets-Sheet 2 United States Patent 0 3,M9,104 STEAM GENERAT- G AND SUPERHEATING UNKTS Uno 0. Bloniqnist, Edmansgatan 5, Vasteras, Eiweden Filed June 6, i953, Ser. No. 740,455 Claims priority, application Sweden June 18, 1957 1 Claim. (iii. 122-4) When starting-up a steam generator condensate may be present or be precipitated in the superheater of the same. This may also occur at other conditions of operation and for instance if the steam generator at stand still periods after operation or starting-up shall be maintained in heated condition in order to be in readiness for rapid delivery of steam large quantities of condensate will precipitate in the superheater due to the fact that the superheater is more rapidly cooled than the active water tube system due to the lower mass of the superheater relative to its heating surface. In itself it is possible to blow the superheater clean by steam but especially at hanging or standing superheater, but from the economical view it is not a practicable way to drain or blow away condensate with steam owing to the large steam quantities required for securing clean blowing of all tube windings. The condensate formed in the very steam conduits can on the contrary be more readily drained by means of condensation water remover in suitably arranged pipings.

Under certain circumstances it is, however, of greatest importance that the superheater is kept free from condensate for instance in power plants Working at high steam pressure. When the steam from the superheater of such plants is used for driving steam turbines one has found that damages can arise in the steam turbine by the condensate carried away from the superheater. Such damages arise especially at the starting of a hot steam turbine operating in a state of readiness.

In steam generators with high working pressure and temperatures for which the invention is especially adapted it is of technical and economical reasons not a practicable way to install water separators in the steam pipings. It is to be noted that modern high pressure steam generators can work at a pressure of 1450 pound per square inch and more and even up to critical pressure and temperatures of 930 F. and more.

The main object of the invention is to keep the superheater free from condensate in an economical way and avoid the above mentioned drawbacks.

Another object of the invention is to provide means for circulating at least the main portion of a hot air or gas stream through or within parts of the gas passes or air and gas passes of the steam generator while externally sweeping over the superheater surfaces. For heating the fluid a source of heat is arranged within the circulation system for the purpose of counteracting the precipitation of condensate in the superheater or remove existing condensate in the same during standstill periods of the steam generating unit during a starting-up period or when the generator is in condition of readiness.

Still another object of the invention is to provide means independent of the normal heating system of the steam generator for producing the hot circulating gas or air.

Another object of the invention is to provide means for producing the circulating gas stream by aid of parts of the normal heating system of the steam generating unit and the gas is recirculated through the superheater and the system of combustion air passes back to the furnace chamber of the generator.

It is desired that the quantity of heat used for heating the superheater is such that the superheater surfaces are always maintained at a temperature somewhat higher than that corresponding to the saturation pressure of the steam.

Efidgddd Patented Aug. Mi, i962 The invention and its foregoing and further objects and advantages will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:

FIGURE 1 is a schematic sectional elevation of a first embodiment of a steam generating and superheating unit provided with improved means according to the invention;

FIGURE 2 is a schematic sectional plan view taken on the line IIII of FIGURE 1;

FIGURE 3 is a schematic sectional elevation of a second embodiment of the invention; and

FIGURE 4 is a schematic sectional elevation of a third embodiment of the invention.

FIGURES l and 2 show a steam generating and superheating unit having a furnace chamber '1 with wall tubes 2 connected to a steam dome or steam and water drum 3. Ducts 4a and 4!; supply combustion air to oil burners 5 in the wall of the furnace chamber. An outlet gas duct 7 from the furnace chamber includes superheater tubes 8 and 8a respectively, which are located in two individual gas passages separated from each other by a partition wall 9. From the steam and water drum 3 conduits 6 lead to the superheater 8, 8a and from said superheater conduits it lead for instance to governor valves of steam turbine or turbines not shown on the drawing.

An economiser 12 is located in the gas passage between the gas duct '7 including the superheater and gas passages 11, 11a leading to the funnel. A heat exchanger of the rotary type possibly arranged in the gas passage is generally designated by 13. The axis of rotation of said heat exchanger is designated by 14. This heat exchanger transfers heat from the heating gases in the passage 11 to the combustion air in the duct 4a.

The embodiment shown in FIGURES 1 and 2 is adapted for circulation of a heating medium through solely or substantially solely the duct 7 including the superheater when the generator is not in operation for instance when the generator is kept in readiness. Said heating medium is circulated by a fan 20 located outside said duct system and in the outlet channel from the fan heating means 22 is arranged. Said heating means 22 may comprise an electric radiator and/ or oil burners or the like. The heated air or gas is passed into the duct 7 at one side of the partition wall 9 and sweeps over the one bank 3 of superheater tubes and then in series therewith the other bank 8a of superheater tubes located on the other side of said partition wall 9 while flowing in the path indicated by the arrows a and b respectively. The air or gas is then recirculated through the channel 23 to the fan 20. If pure electric heating is used additional air need not be supplied to the circulation system. If the heating is carried out by aid of oil burners combustion air must be supplied and may be supplied in controlled rate for instance through the conduit 24 and upstream the fan 20 or directly at the oil burner or burners. In this case the excess of burned gases must be withdrawn and this is eifected in this embodiment through the economiser 12 to the gas pass 11. The excess of gas may be conducted as shown by arrow 0 to the portion lla of the gas pass and the funnel through a by pass conduit 26 while not passing the heat exchanger 13. In this case the dampers 27, 23 in the main pass are shut and the damper 29 in the by-pass conduit is open. Possibly the excess of gas may instead be conducted through the heat exchanger 13 and the dampers 27, 28 and 29 are correspondingly adjusted. Even with electric heating of the circulating air, if it is considered suitable, one may supply excess of air through the conduit 24- and said excess of air may then be used for heating the heat exchanger.

The flow of hot air or gas through the gas duct 7 may be reversible, for instance automatically reversible so that the heating medium alternatingly flows in the direction of the arrows at and b and in the reversed direction. This may be carried out by means of shifting valves and conduits between the conduits 23 and 21.

In order to secure the removal of condensate evaporated in the superheater when the temperature diiference between the water contents in the steam dome 3 and the superheater is small it is suitable to include a condenser surface in the active tube system. In the embodiment shown a condenser 80 is provided for said purpose in the conduit 6. The condensed water may be recirculated through the conduit 31 to the steam dome or a suitable collecting place in the feed water system. The condenser may instead or at the same time be located in the conduit 1t upstream of the governor valve of the turbine or turbines.

In FIGURE 3 the same numbers as in FIGURES 1 and 2 are used for corresponding details. In this embodiment the external heating means 22 which may still be electrically heated or heated by oil burners is also used for keeping the furnace hot when the steam generating and superheating unit is in condition of readiness. The hot air or gas produced by the heating means 22.- is conducted through the conduit 21 and the branch conduits 21a to the gas duct 7 and the superheater surfaces 8 and is then passed into the furnace chamber 1 in the direction of the arrows d and e. From the furnace chamber 1 the circulating stream may be lead into the air duct system 4b, 4a through the air supply openings in the burners 5 and driven backwards in the direction of the arrow 1 through 5 the air preheater 13 and through an opening 35 and an opened damper 36 in the direction of the arrow g through a conduit 37 back to the circulation fan 20. The dampers 27, 28 and 38, 39 are in this case shut. In the case said means 22 is heated by oil burners excess of gas may be withdrawn for instance through the gas pass 11, and by adjusting damper 39, may be passed to the tunnel or induced draught fan respectively.

According to another embodiment the circulation stream for keeping the superheater hot may be heated by parts of the ordinary heating system of the steam generator and portions of the produced gas quantity are circulated through the superheater and a portion thereof is recirculated to the furnace chamber suitably through the normal duct system for the combustion air. Such an arrangement may also be explained set out from FIGURE 3. In this case the external heating means 22 is not present the fan 20, however, being retained for the circulation flow.

In this case it is sufficient to fire the steam generator with only one or some of the burners 5. Combustion air is supplied for instance upstream the fan 20 and the air and gas stream flows in opposite relation to the arrows d, e, f, g. After the hot gas stream having swept over the superheater surfaces it is conducted through the fan 20. The excess of gas is withdrawn through the gas pass 11a and the damper 39 while a portion of the gas stream in the pass 40 provided with a damper or through the opening is recirculated through the duct 4a, 4b to the furnace chamber. The damper 38 is in this case shut while the damper 4 1 is open and the damper 42 shut.

In FIGURE 4 a further embodiment of an arrangement according to the invention is shown. In this case a gas or air stream heated outside the steam generator is used for keeping the superheater in hot condition and simultanously keeping the furnace chamber in hot condition. In this embodiment 45 designates the normal air supply conduit to the burners 5. In this conduit a damper 46 is provided and down-stream said damper a conduit 47 leading to the fan 20 is connected with said first mentioned conduit 45. In the outlet conduit 48 from the fan there is provided heating means 22, an electric radiator or for instance an oil burner with separate air supply. The conduit 48 is connected to the normal outlet side of the gas duct 7 in which duct the superheater is hanging. To the conduit 48 there is connected a conduit 49 provided with an adjustable damper and adapted to discharge the excess of gas to the funnel. The normal furnace gas pass is designated with 5&1 and is provided with a damper 52. When the heating means operates the air or gas circulates in the direction of the arrows p firstly through the superheater and secondly through the furnace chamber and then through the air intake to the burner or burners 5 back to the fan 20.

I claim:

In a high temperature and high pressure steam generating and superheating system, in combination, a steam generator, a superheater, steam conduit means having a connection with said generator with said superheater; means for preventing precipitation of condensate in the superheater during stand-still periods and maintaining said superheater in condition of readiness, said means comprising water-condensing and collecting means connected in said steam conduit means between said generator and said superheater, means for removing water collected by said water-condensing and collecting means; said superheater having a gas passage, a partition wall in said superheater extending from one end of said superheater toward but not as far as the other end thereof, said superheater having two parallel banks of steam conduits located respectively on opposite sides of said partition, said connection of said steam conduit means with said superheater comprising connections with said banks of steam conduits, a gas conduit connected with said superheater gas passage toward the end thereof from which said partition extends, a return gas conduit connected with said superheater gas passage toward the same end as said first-mentioned gas conduit on the opposite side of said partition, said return gas conduit being connected with said first-mentioned gas conduit, thereby forming, with said superheater gas passage, a circuit for recirculation of gas, means in said first-mentioned gas conduit for introducing a stream of gas into said gas passage, means within said first-mentioned gas conduit for heating the introduced gas stream sutficiently to impart to the superheater a temperature above the temperature of saturation of the steam generator.

References Cited in the file of this patent UNITED STATES PATENTS 1,872,138 Grady Aug. 16', 1932 2,685,866 Yost Aug. 10, 1954 2,879,751 Lieberherr Mar. 31, 1959 FOREIGN PATENTS 523,871 Great Britain July 24, 1940 548,260 France Oct. 16, 1922 

